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Optische und elektronische Eigenschaften von AlGaN/GaN-Heterostrukturen
| Content Provider | Semantic Scholar |
|---|---|
| Author | Winzer, Andreas |
| Copyright Year | 2009 |
| Abstract | The electronic material properties of AlGaN/GaN heterostructures were investigated. The analysis of optical spectra by complex models allowed for the first time to confirm the theoretically predicted dependence of the polarisation discontinuity (also called polarisation charge) on the Al content by reliable experiments. Furthermore, it is shown that the polarisation discontinuity is constant over the temperature range from 5 K up to room temperature. The method employed here is based on the analysis of electroreflectance (ER) spectra and exploits the specific dependence of the electric field strength within a layer on the applied electric voltage. In this work this method is consequently refined to surpass all alternative methods in accuracy. ER spectra of group-III-nitrides posses some general peculiarities: (i) In direct proximity to the band gap they can not be described by constant Seraphin coefficients in contrast to small gap semiconductors (e.g. GaAs). (ii) Though, the analysis of the Franz-Keldysh oscillations by Aspnes' method yields the correct values of the electric field strength as it is the case for small gap semiconductors. Optical and especially ER spectra of group-III-nitrides can only be described completely by taking into account for excitons in electric fields. For this a model proposed by Blossey was applied to nitride semiconductors and implemented into a software program. By extensive numerical simulations it was found that the energetic position of the exciton main resonance as well as its spectral width depend linearly on the electric field strength. The approach presented is unique since it allows for a quantitative description of excitons in inhomogeneous electric fields. The good agreement between experiment and simulation supports the reliability of the material properties presented in this work. The operation of AlGaN/GaN heterostructures as chemical sensors was investigated by means of optical spectra too. If Pt contacted samples have been exposed to hydrogen the density of their two dimensional electron gases were raised by several 10e/cm while the Schottky barrier heights were lowered by up to 0.85 V. Wetting of the free surface of not contacted samples by a polar liquid (acetone) led to an increase of the surface potential and a decrease of the net surface charge density. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.db-thueringen.de/servlets/MCRFileNodeServlet/dbt_derivate_00016771/ilm1-2009000403.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
